This invention relates to an electrical control for a bi-directional motor which incorporates a defroster element.
Many modern vehicles include a rear window defroster and a rear window wiper. Typically, the rear window defroster consists of a power switch and a resistive electrical filament strip bonded to the inside of the rear window. One end of the resistive filament is connected to a power source and the opposite end of the resistive filament is connected to ground. When the defroster is switched on, current from the power source flows through the resistive filament to ground thereby warming the filament. The warm filament heats the rear window.
Many modern vehicles further include a single rear window wiper. A wiper arm is moved in a reciprocating motion across the rear window by a bi-directional motor. Typically, the bi-directional motor is driven with a H-bridge drive. The H-bridge drive operates to apply current in alternating directions across the motor. Prior art H-bridge drives have employed a variety of electrical components and have taught several different designs or lay-outs.
One particularly advantageous type of H-bridge uses a pair of current dissipating resistive elements. Typically, a pair of power resistors would be used. The power resistor could operate as a pull-up resistor connected in series between the current source and the motor or a pull-down resistor connected in series between the motor and ground. Power resistors dissipate power by giving off heat. This type of H-bridge has typically not been used for rear wiper motors, as the necessary power resistors would be too large to be practical. Thus, other H-bridge designs have been used which may have some undesirable characteristics.
In most modern vehicles, the rear window defroster and the rear window wiper system are packaged close to each other yet assembled and operated separately. It would be desirable to capitalize upon the packaging proximity and integrate the rear window defroster system and the rear window wiper system to reduce parts, conserve packaging space, decrease cost, and increase reliability. Further, it would be desirable to use the heat generated by the H-bridge drive to warm the rear window.
Side-view mirrors are also being provided with defroster elements and controls, and separate controls for positioning motors.